Activities related to pollutant emissions were applied to multiple regressions and seasonal decomposition for extracting hourly and monthly emission variations used for atmospheric models. The results of the analyses were used for evaluating emission changes during the COVID-19 pandemic. The activities used for the analyses were thermal powers, energy consumption of stationary sources, and travel distance of motor vehicles. Hourly variations were high from 9 to 18. Weekly variations were high from Tuesday to Friday. Monthly variations were low in May and October, May and June, and February for thermal powers, energy consumption, and travel distance, respectively, and high in December and January. Reductions during the COVID-19 pandemic were evaluated by activity differences between 2019 and 2020. Annual relative differences were −1.5, −10, and −8.0% for the thermal powers, energy consumption, and travel distance, respectively. Those in a state of emergency months, i.e., April and May, were −9.0, −13, and −18%, respectively. The annual relative differences in the spatial means of the NO_x and PM_2.5 concentrations on the ground were −6.8 and −7.5%, respectively. Those in April and May were −13 and −11%, respectively. Reductions of the activities during the COVID-19 pandemic were comparable to those of the related chemical measurements.